If you're going to be using the amp for the majority of the day at various times, leave it on in standby mode. If you aren't going to use it for very long each time and / or have extended periods between use, turn it off and on as needed using your own judgment.
Tubes deteriorate with use, even in standby mode with most designs. Not only that, but some tubed amplifier designs can become hazardous / start on fire when a tube fails. As such, i would not leave tubed amplifiers on and unattended for extended periods of time. Obviously, this is my point of view, so take it for what it is worth.
I say this because most properly designed tubed circuits with reasonably strong tubes stabilize in appr 20 - 30 minutes of use. There is little to no sonic benefit in leaving a tubed power amp fired up 24/7 other than the reduction of in-rush current to the tubes.
Bare in mind that i'm talking about output level tubes here, NOT line level tubes such as found in a preamp, CD player, DAC, etc... The voltage and current levels found here are MUCH lower, hence leaving them fired up is far more benign with less potential for major problems. Sean
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